Start by making a list of what you would like the room to include: size, windows, flooring etc. Then find a trusted architect to do the plans.

As chookchook said in her recommendation about painting, put a drop cloth on the floor. Get a very safe ladder. remove the lightbulbs, and cover the outlets. Turn off the electricity to the chandelier. Then spray it with a mild cleaner (I use one I found at Target that's basically water with vinegar, until it's dripping wet. Start at the bottom and work your way up, so you don't have dirty spray dripping on the bottom of the chandelier.Work your way up and down until the dripping spray is clean. The chandelier may be gorgeous and expensive, but it seems totally out of place in the architecture of the room--more at home in a chalet than a sunny room with a window wall. I would probably try to find a way to get it removed, and sell it to someone who appreciated it better than I.

No suggestions here apart from getting the wallpaper you want either shipped to you or searching around for it!

I would clean up first. Especially the stuff growing in the paving. Then get gardening with pot plants and start experimenting with different plants and the positions. See what you like and if you can keep it alive! Our house has the sun setting over the back fence and we've done a few inexpensive things to reduce that issue (most expensive were outdoor blinds around the verandah) but for most of the year we just don't want to be out there. It is hard work to keep the plants going in summer, there is a lot of sand due to the difficulty in keeping lawn alive and it is just bloody hot. So, that's why I'm saying clean up, start gardening small and see how you go before committing to structures that might not address the real issues you have with the yard. Just my 2 cents! :)